2005 Sierra 1500 Cooling Issue

First of all, hello all, first time poster, so bear with...
I have a 5.3 engine with a cooling problem. It started off by just a mystery leak somewhere. Not a bad leak, just a couple of quarts every month or so. This has progressed into an overheating issue. I was a gradual thing, slight overheating then cooling down and running normal for a while. It has progressed to where it spikes after just a couple of miles. Here is what I have done so far:

Thermostat (tried running with and without just in case it was a bad replacement part)
Check oil - no coolant
pressure test - 10 minutes at 18psi with no loss.
Flushed radiator
Talked very nice to engine, asking it to please behave
Talked not so nice, threatening very unpleasant things if it not behave

First of all, hello all, first time poster, so bear with...
I have a 5.3 engine with a cooling problem. It started off by just a mystery leak somewhere. Not a bad leak, just a couple of quarts every month or so. This has progressed into an overheating issue. I was a gradual thing, slight overheating then cooling down and running normal for a while. It has progressed to where it spikes after just a couple of miles. Here is what I have done so far:

Thermostat (tried running with and without just in case it was a bad replacement part)
Check oil - no coolant
pressure test - 10 minutes at 18psi with no loss.
Flushed radiator
Talked very nice to engine, asking it to please behave
Talked not so nice, threatening very unpleasant things if it not behave

Any ideas?

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Have check for leaking at the Water Pump, and that's just a guess.....:neutral:

this is the deal buddy. you have a leak. adding 2 qts of coolant is a big deal. since you cannot find the leak location I would add some bars coolant stop leak. premix some in the coolant drained from the radiator. remove top radiator hose at the radiator , add the sealer pre -mix into the hose then install hose and fill the coolant plastic pressure tank with no sealer just coolant/antifreeze. run until hot with the pressure cap off and rev a few times to remove air. see if the overheating air pocket / losse of fluid stops.

this mystery leak is usually the water pump engine gaskets. re-torque the water pump bolts also along with the bars sealer..

I will give that a try. Even the guys at the parts store was scratching their heads. They didnt even want to sell me parts until i was sure it wasnt a waste of money just trying things. Will let you know how it goes. Thanks for the advice.

I will give that a try. Even the guys at the parts store was scratching their heads. They didnt even want to sell me parts until i was sure it wasnt a waste of money just trying things. Will let you know how it goes. Thanks for the advice.

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this will work most times with this type leak. sure if its a head gasket no but the other areas it has worked very well. don't forget to snug down those WP studs...

I don't see why a good, stern, talking to didn't work! I think that works best for me! But was it for the dogs, the wife, or the truck!?!? OH wait, its for how the wife fixes things with me!!!!!!

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I have to disagree with Jcat on one thing! Re-torqueing the water pump bolts is a risky move that might not play out like you would hope! That's just my HO.!

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I have found that with the water pump very large and the bolts very small in diameter but long, the bolts stretch and loosen after several years. re-torque to about 18 ft lbs. I am sure some will be loose.